1. Field of the Invention
The present invention is directed to an improvement in a method for the inhibition of the polymerization of styrenic monomers wherein the inhibitor comprises a sulfonic acid.
2. Description of Related Art
Many ethylenically unsaturated monomers undesirably polymerize at various stages of their manufacture, processing, handling, storage, and use. Polymerization, such as thermal polymerization, during their purification results in the loss of the monomer, i.e., a lower yield, and an increase in the viscosity of any tars that may be produced. The processing and handling of the higher viscosity tars then requires higher temperature and work (energy cost) to remove residual monomer.
Polymerization can also result in equipment fouling and losses in production efficiency owing to the deposition of polymer in or on the equipment being used. These deposits must be removed from time to time, leading to additional loss in production of the monomer.
A wide variety of compounds has been proposed and used for inhibiting uncontrolled and undesired polymerization of ethylenically unsaturated monomers. However, many of these compounds have not been fully satisfactory.
U.S. Pat. No. 2,867,672 discloses that the polymerization of uninhibited styrene condensing in liquid form on the surfaces containing the vapor space above the liquid level of the main body of styrene in a tank may be minimized, by spraying the surfaces enclosing the vapor space with a styrene polymerization inhibitor.
U.S. Pat. No. 4,086,147 discloses a process for the distillation of readily polymerizable vinyl aromatic compounds comprising subjecting a vinyl aromatic compound to elevated temperatures in a distillation system in the presence of a polymerization inhibitor comprising m-nitro-p-cresol.
U.S. Pat. No.4,468,343 discloses a compound and a process for utilizing the compound to prevent the polymerization of vinyl aromatic compounds, such as styrene, during heating. The composition includes effective amounts of 2,6-dinitro-p-cresol and either a phenylenediamine or 4-tert-butylcatechol respectively, to act as a polymerization co-inhibitor system in the presence of oxygen.
U.S. Pat. No. 5,254,760 discloses the inhibition of the polymerization of a vinyl aromatic compound, such as styrene, during distillation or purification by the presence of at least one stable nitroxyl compound together with at least one aromatic nitro compound.
U.S. Pat. No. 5,290,888 discloses a process for stabilizing an ethylenically unsaturated monomer or oligomer from premature polymerization whereby a stabilizing amount of an N-hydroxy substituted hindered amine is added to said polymerizable monomer or oligomer. The ethylenically unsaturated monomer or oligomer encompasses vinyl monomers or oligomers bearing at least one polymerizable moiety. The N-hydroxy substituted hindered amine is said to inhibit premature polymerization in the liquid and/or vapor phase.
U.S. Pat. No. 5,446,220 discloses methods for inhibiting the polymerization of vinyl aromatic monomers in oxygen-free processing systems. These methods comprise adding from 1 to about 10,000 parts per million parts monomer of a combination of a dinitrophenol compound, a hydroxylamine compound and a phenylenediamine compound. Preferably, 2-sec-butyl-4,6-dinitrophenol or 4,6-dinitro-o-cresol are used in combination with bis-(hydroxypropyl)hydroxylamine and N,N′-di-sec-butyl-p-phenylenediamine.
U.S. Pat. No. 5,932,735 discloses that selected derivatives of 1-oxyl-2,2,6,6-tetramethyl-4-hydroxypiperidine are effective as inhibitors to prevent the premature polymerization of acrylic and methacrylic acids, their esters, their amides, vinyl acetate and acrylonitrile in the presence of water.
U.S. Pat. No. 6,143,205 discloses a mixture for inhibiting the premature polymerization of monomers that contains (A) vinyl-containing monomers, and (B) an effective amount of a mixture of (I) from 0.05 to 4.5% by weight, based on the total mixture (B), of at least one N-oxyl compound of a secondary amine which carries no hydrogen atoms on the .alpha.-carbon atoms and (ii) from 99.95 to 95.5% by weight, based on the total mixture (B), of at least one nitro compound.
U.S. Published Application No. 2004/0147797 discloses a process for inhibiting the polymerization of an aromatic vinyl compound which is capable of efficiently inhibiting the polymerization of an aromatic vinyl compound not only in an initial stage but also over a long term in the stage of producing, purifying, storing or transporting the aromatic vinyl compound, and which is said to be excellent in handling. The process comprises adding 2-nitrophenol compound in combination with a sulfonic acid compound to the aromatic vinyl monomer during the stage of producing, purifying, storing or transporting the aromatic vinyl compound.
The foregoing are incorporated herein by reference in their entirety.